Alkanes
2 marks · HardThe molecular formula for an alkane with 16 carbon atoms is C₁₆H₃₄. State the general formula for alkanes. Using this formula, explain how you can determine the number of hydrogen atoms in any unbranched alkane.
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Also accept: CnH2n+2; C_nH_{2n+2}; C\_nH\_{2n+2}
Common mistakes: Giving formula for alkenes; Incorrect interpretation of n
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Marking points
B1 · 1 mark · States the correct general formula: , , or equivalent
B2 · 1 mark · Correctly explains that the number of H atoms is found by multiplying the number of C atoms by 2 and adding 2 (i.e., using the general formula to calculate H for a given n)
Worked solution
The general formula for alkanes is .
To determine the number of hydrogen atoms in any unbranched alkane, multiply the number of carbon atoms by 2 and add 2. That is, if an alkane has carbon atoms, it has hydrogen atoms.